Over the past ten years, tremendous progress has been made in understanding hearing processes in the budgerigar. What is lacking, is an understanding of how these auditory processes are related to the characteristics of species-specific vocal signals, produced by budgerigars. The present research plan will remedy this situation by: (1) examining the acoustic variability of natural budgerigar vocalizations, (2) determining the effect of auditory isolation on the development of a normal vocal yepertoire on this species, (3) determining the effect of both early and late deafening on the development and maintenance of a normal vocal repertoire, and (4) measuring the limits of vocal learning using computer-synthesized vocaliizations as training stimuli. Drawing on newly-developed acoustic analysis techniques, standard ethological procedures, and an effecient psycho-physical method for testing auditory capability. it will be possible to specify with considerable precision the contribution of both innate and environmental factors both of which are known to influence the development of speech in humans. The proposed research program offers an excellent model for testing directly the contributions of each factor. The budgerigar model, where vocal learning is an essential feature of the organism's developmental biology and is more closely tied to complex social interactions between family and non-family member, offers the possibility of an even stronger parallel with human vocal communication than has been the case with other avian species. In developing an animal model for the ontogeny of a vocal learning system, the search is for general biological principles involved in human speech perception, phonological development, and language acquisition. The budgerigar model will allow tests of theories of the role that learning plays in the behavior for maintaining a complex social structure. Experimental manipulation of both sensory, social, and biological aspects of this process will provide unique insight into general biological mechanisms that operate during ontogeny to produce a complex vocal repertoire for social communication.